Method and apparatus for distributorless ignition

ABSTRACT

Means for directing a spark from the secondary winding of a spark coil to one of two spark gaps connected thereto. The primary winding of the coil can be connected to a battery so that the core of the coil is magnetised in either one of two directions. Depending on this direction, one or the other of the two spark gaps is fired, by series or shunt diodes. Means are provided for damping out undesirable oscillations which may occur when the primary circuit is broken.

United States Patent [1 1 [111 3,910,247 Hartig Oct. 7, 1975 [5 METHOD AND APPARATUS FOR 3,677,253 7/1972 Oishi et al. 123/148 DC DISTRIBUTORLESS IGNITION Gunter Hartig, Hansastrasse 29, Karlsruhe 21, Germany, D-750O Filed: Mar. 25, 1974 Appl. No.: 454,737

Inventor:

Foreign Application Priority Data July 25, 1973 Switzerland 10884/73 U.S. Cl 123/148 E; l23/8.07; 123/148 DS Int. Cl. F02P 3/06 Field of Search 123/148 E, 8.07, 8.09,

l23/8.45, 148 DS, 148 DC References Cited UNITED STATES PATENTS Kaehni 123/148 E Primary Examiner-Wendell E. Burns Assistant Examiner.lames Winthrop Cranson, Jr. Attorney, Agent, or FirmToren, McGeady and Stanger [5 7] ABSTRACT Means for directing a spark from the secondary winding of a spark coil to one of two spark gaps connected thereto. The primary winding of the coil can be connected to a battery so that the core of the coil is magnetised in either one of two directions. Depending on this direction, one or the other of the two spark gaps is fired, by series or shunt diodes. Means are provided for damping out undesirable oscillations which may occur when the primary circuit is broken.

24 Claims, 11 Drawing Figures US. Patent Oct. 7,1975 Sheet 1 of4 3,910,247

U.S. Patent 0a. 7,1975 shw 2 0M 3,910,247

Fig. 3

Fig.4u Fig.4b Fig.4c Fig.4d

U.-S. Patent Oct. 7,1975 Sheet 3 of4 3,910,247

US. Patent Oct. 7,1975 Sheet 4 of4 3,910,247

METHOD AND APPARATUS FOR DISTRIBUTORLESS IGNITION The present invention concerns a method and apparatus for cyclic distributorless ignition of high tension pulses to the cylinders of internal combustion engines.

By distributorless ignition, such ignition is to be understood, in which the high tension pulses to be distributed to spark plugs are not distributed through an ignition distributor located in their path of transmission, to the individualplugs. Such distributors are extremely sensitive to moisture, soiling and the like; due to burning of the distributor contacts, they are subject to intense wear and the longer they are used, the more inaccurate and unreliable they become.

Although distributorless ignition systems already exist in accordance with the above definition, in which the distribution of the voltages and currents constituting the high tension pulses is effected on the primary side of the ignition coil by means of a plurality of circuit-breakers, a separate ignition coil is required in this case for, at most, two spark plugs which have to be ignited simultaneously; i.e. for a 4-cylinder engine, two ignition coils are necessary, a feature which is relatively expensive and requires a comparatively large amount of space for the ignition system.

It is an object of the present invention to provide a method and apparatus for distributorless ignition which is less expensive and, more particularly, requires less space for the ignition system.

According to the present invention there is provided a method of distributorless cyclic ignition more particularly for internal combustion engines, in which an energy source produces a high tension pulse across at least two spark gaps sequentially, characterised in that a current is caused to flow for a period alternately in one direction and then in the opposite direction, through the primary of a high tension transformer (ignition coil) the current being interrupted between two successive periods during which the energy source is at least partially discharged alternately in one direction and, after the following interruption of the current flow, in the opposite direction, at least one pair of spark gaps being disposed in the discharge circuit of the energy source, one of the two spark gaps of a pair being blocked or short circuited-during current flow in one direction whilst the other gap is blocked or short circuited during current flow in the other direction.

Apparatus for carrying out the method of distributorless ignition according to the invention comprises, a circuit arrangement on the primary side of a high tension coil constituting an energy'source and/or charging it, the circuit being such that a current flows first in one direction and second in the opposite direction in the primary winding, the current being interrupted between two successive periods of current, the energy source output having at least two spark gaps and at least one blocking and/or one short-circuiting means which blocks or short circuits the discharge current during the discharge of the energy source in one direction to the first spark gap so that only the second spark gap fires, and similar but oppositely polarised means for the second gap so that during the discharge current including a single ignition coil and, at the same time, to obtain the advantage of a distributorless ignition system resulting in the elimination of the abovementioned disadvantages of ignition distributors.

The above and other advantages and features of the present invention are described in greater detail hereinafter with reference to some embodiments illustrated in the accompanying drawings in which:

FIG. 1 shows a scematic circuit diagram explaining the basic principle of the present invention, and also shows a first embodiment of the present invention;

FIG. 2 shows a second embodiment of the invention;

FIG. 3 shows a third embodiment of the invention;

FIG. 4 shows several possible embodiments of the clamping member connected in parallel with the primary side of the ignition coil,

FIG. 5 shows a graph of the voltage to a time base, explaining the mode of operation of the damping member according to FIG. 4f; and

FIG. 6 shows graphs of currents and voltages explaining the circuit arrangement according to FIG. 3 in conjunction with the clamping member of FIG. 4d.

Reference is now made to FIG. 1, from which the principle of the present invention may be seen.

In this case, the primary winding 1 of an ignition coil 2 is connectable at one end 3, through two parallel switches 4 and 5 either to a positive voltage U,,, or to a negative voltage U other end 6 of the primary winding 1 being earthed. The secondary winding 7 of the ignition coil 2 is connected at one end 8, through a first diode, to the high tension socket of a first spark gap 10 the other side of which is connected to earth; in addition, the end 8 is also connected to the high tension socket of a second spark gap 12 via a second diode 1 1 connected in reverse polarity to the first diode; the other end 13 of the secondary winding7 is earthed and thus the secondary circuit is completed.

In the primary winding 1 of the ignition coil 2, a flow of current is produced alternately in one direction and then in the other opposite direction, each flow being interrupted by switching off the flow of current by the respective switch. This means that, a current is first produced in the primary winding 1 from connection 3 to connection 6; this current is then switched off and a current caused to flow through the primary coil 1 in the reverse direction from connection 6 to connection 3, this current being itself switched ofi. The cycle is repeated. Induced Current in the secondary circuit at the time in which the primary winding 1 is first switched off is applied to one spark gap 10 only in a pre-determined direction, the other spark gap 12 receives current in the opposite direction, during the second switch off.

When the switch 4 is closed, the positive voltage U is applied to the connection 3 of the primary winding 1, so that a current flows through the primary winding from connection 3 to connection 6. When-the switch 4 is opened, the connection 8 receives a negative hightension pulse which traverses the diode 11; diode 9 is non-conductive, so that a spark discharge occurs only at the spark gap 12. If the switch 5 is then closed and opened, negative voltage U is applied to the connection 3, so that the flow of current in the primary winding 1 now takes place in the opposite direction from connection 6 to connection 3. When the switch 5 is opened apositive high tension voltage is now produced on the connection 8 and traverses diode 9 to produce a spark discharge in the spark gap 10, whilst clue to the blocking action of the diode l 1, no spark discharge can take place at the spark gap 12.

It is not necessary to provide both a positive and a negative voltage source simultaneously in order to cause the current to flow alternately in opposite directions in the primary winding; two double-pole contactors may be provided, connected to only one voltage source, the operation of one contactor causing current to flow through the coil primary in one direction, preferably the other contactor causing a reverse flow. An alternative, shown in FIGS. 2 and 3, is to provide the primary of the ignition coil with a centre tapping 14, respectively, connect the tapping to one pole of the voltage source, and connect the ends of the primary alternately to the other pole, which may be earthed, of the voltage source.

FIG. 2 shows the basic embodiment of an ignition system for a two-disc rotary piston engine: a cam 17 mounted on a shaft 16 closes circuit breakers l8 and 19 at points 180 apart. These circuit breakers, together with resistors 20 and 21, are so connected to transistors 22 and 23, that only one of the two is conductive at a time, and both transistors are blocked for a certain time between the change-over from one transistor to the other. The primary winding 24 of the ignition coil 25 has a push-pull winding, the centre point 14 of which is connected to the supply voltage U Since one transistor 22 connects one end 26 and the other transistor 23 the other end 27 of the primary winding 24, when in the switched-through condition, to the other earthed pole of the voltage source current flows take place, alternately in one direction and the other in the primary winding 24, interrupted by periods in which both transistors are blocked. Since, consequently, the magnetic field in the ignition coil 25 has a different direction according to whether transistor 22 or transistor 23 is conducting, a voltage pulse is produced in the secondary winding 28 when the primary current is switched off the polarity of which pulse depends on which transistor has been conductive. The high tension diodes 29 and 30 which are connected between earth and respective ends of the secondary winding 28 of the ignition coil and in parallel with spark gaps 31 32 also connected between the ends of the secondary winding 28 and earth, are so polarised that only one of the two spark gaps 31 or 32 can flash over, depending on the polarity of the induced secondary pulse.

Diodes 33 and 34 are inserted between ends 26 and 27 and their associated transistors 22 and 23. These diodes are polarised so that they prevent conduction of the transistors 22 and 23 under reversed polarity when a negative voltage peak is produced on the other part of the winding 24 upon the collapse of the magnetic field in the ignition coil, as a result of the switching off of the other transistor 22 or 23.

FIG. 3 shows an embodiment of the present invention for a 4 cylinder engine. As in the embodiment of FIG. 2, a magnetic field is produced first in one direction and then in the other in the ignition coil 35 through transistors 36 and 37 and the push-pull primary winding 38 so that in this respect no further description is necessary. Again, the diodes 39 and 40 correspond to the diodes 33 and 34 in FIG. 2.

However, the control of the transistors 36 and 37 differs from that of FIG. 2. These transistors receive their control voltages through control connections 41 and 42. The control voltage for the transistors 36, 37 is kept to a predetermined level by means of the zener diodes 43, 44 connected in parallel with the control voltage, in conjunction with the series resistors 45, 46 so that the magnetising current in the primary winding 38 of the ignition coil 35 has a value independent of the operating voltage, in consequence of the bias resistors 47, 48 in the emitter circuits. At the switching-off of a transistor control voltage a voltage pulse whose polarity depends on which of the transistors 36 or 37 has been conductive, is produced in the secondary winding 49.

One end 50 of the secondary winding 49 of the ignition transformer 35 is connected to a first spark gap 52 through a first diode 51; a second diode 53, with reversed polarity compared with the first diode 51, is connected to a second spark gap 54. The other end 55 of the secondary winding 49 is connected to a third spark gap 57 through a third diode 56 polarised in the same manner as the first diode 51, and through a fourth diode 58 polarised in the same manner as the second diode 53, to a fourth spark gap 59. The other ends of the spark gaps are connected in the normal manner to earth.

In the case of a positive voltage peak at the point 50 of the secondary winding 49, the diodes 53 and 56 are conductive, causing sparks at spark gaps 54 and 57. In the case of a negative pulse peak at 50, the diodes 51 and 58 are conductive, whereby spark gaps 52 and 59 are energised.

The clamping member 60 in FIG. 3, which is connected by its connections 61 and 62 between the ends of the primary winding 38, dampends undesirable resonance oscillations. Embodiments of damping members are shown in FIGS. 4a to 4f. The reduction or suppression of such resonance oscillations of the primary current is important, because changes of primary current direction and hence secondary voltage could fire a complementary spark gap at an undesired moment.

All the above described damping members in FIGS. 4a to 4f are connected in parallel with a primary winding 1, 24, or 38 or with a part thereof. Alternatively a separate damping winding may be provided on the ignition coil to co-operate with the damping member. FIG.

4a shows an ohmic resistor which may be damping or loss-involving material in the core of the ignition coil.

FIG. 4b shows a voltage-dependent resistor (VDR), FIG. 40 shows a capacitor and FIG. 4d shows a triac, the control electrode 63 of which is energised by an auxiliary pulse at the beginning of the second current half-wave after the collapse of the magnetic field in the ignition transformer; the triac fires and short-circuits any following resonance oscillations, a feature which is described in greater detail below in connection with FIG. 6.

In this figure, I indicates the control current of the transistor 36, whilst 1 is the control current of the transistor 37. U.,,, is the voltage induced in the secondary winding 49, assuming no damping member 60 is provided in FIG. 3. U is the control voltage of a triac FIG. 4d which is provided as clamping member 60 in FIG. 3. U is the voltage from the secondary winding 49 with the above triac acting as clamping member. Finally, U is the voltage across the spark gaps 54 and 57 and U the voltage across the spark gaps 52 and 59.

The transistor 36 is switched on by control current I at the time t, and switched off at the time As a result of this switching off, several voltage peaks 64 67 succeeding each other with alternating polarity and decreasing in height, would occur across the secondary winding 49, beginning with a positive voltage peak, if no damping member is used. If a firing voltage U is applied to the control electrode 63 of the triac either directly or through an alloy network, so that it ignites the triac at the time t when the first voltage peak 64 ends, then only a positive voltage peak 64 is derived from the secondary winding 49. The duration of the control voltage pulse 93 is such that any voltage peaks 65, 66, 67, are suppressed, and a single positive ignition voltage pulse 68 is obtained across the spark gaps 54 and 57. The same applies to the production of a single negative ignition voltage pulse 69 across the spark gaps 52 and 59.

FIG. 4e shows a damping member in which a triac in a conventional dimmer circuit fires after a time determined by the resistor 71 and the capacitor 72; the diac 73 short circuits the resonance voltage after firing.

FIG. 4f shows a circuit which short-circuits the resonance oscillations when the voltage of the main ignition pulse 74 has died away to a low voltage value. This is achieved by a bridge circuit 75 which rectifies the alternating pulse voltages 74, 76, 77, 78 (FIG. 5). These rectified pulses 79, 80, 81, 82 which appear at the output connections 83, 84 of the bridge circuit Ug3 84, are integrated to a voltage value U, on the capacitor 86 (point U, of the voltage U on the capacitor 86, FIG. 5) in the RC combination connected in parallel with the said output connection and comprising a resistor 85 and a capacitor 86 connected in series therewith. As soon as the output voltage U of the bridge rectifier has dropped to approximately this integrated voltage value (at the time t in FIG. 5) junction transistor 88 connected in series with resistors 89, 90 conducts since its ignition electrode 91 is connected to the junction of capacitor 86 and resistor 85. The junction transistor is also connected to the thyristor 87 in such manner that, upon ignition, it in turn fires the thyristor 87, so that the resonance oscillations 76, 77, 78, following the main pulse 74 are suppressed.

The ignition of the thyristor is effected by the voltage pulse 92 of the voltage U appearing across the resistor 90. This voltage pulse is made of such duration by suitable dimensioning of the resistor 85 and the capacitor 86 that it overlaps the entire remainder of the resonance oscillation (up to 1 in FIG. 5).

I claim:

1. A method for distributorless cyclic ignition of an internal combustion engine by sequentially producing from an energy source high tension pulses across a plurality of spark gap means comprising the steps of alternately inducing current to flow in a first and in a second direction in the primary winding of a high tension ignition coil, interrupting said current flow between each change of direction of said flow from either one of said directions to the other, providing at least one pair of spark gap means connected in circuit with a secondary winding of said high tension ignition coil, blocking current flow to one of said spark gap means while enabling current flow to the other of said spark gap means when said secondary winding has induced therein current flow in a given direction, and blocking current flow to said other spark gap means while enabling current flow to said one spark gap means when the direction of current flow through said secondary winding is reversed.

2. A method according to claim 1 wherein a plurality of pairs of spark gap'means are provided and wherein current flow is blocked to one of the spark gap means of each of said pair while enabling current flow to the other spark gap means of each of said pair when said secondary winding has induced therein current flow in a given direction, and wherein current flow is blocked to the other spark gap means of each of said pairs while enabling current flow to said one spark gap means of each of said pairs when the direction of current flow through said secondary winding is reversed.

3. A method according to claim 1 including the step of damping resonant oscillations in said high tension coil.

4. A method according to claim 3 wherein said damping of said resonant oscillations is performed in a primary circuit including the primary winding of said high tension coil.

5. A method according to claim 4 including the step of short-circuiting the primary circuit including said primary winding of said high tension coil during the appearannce of undesirable resonant oscillations therein.

6. Apparatus for effecting distributorless cyclic ignition of an internal combustion engine by sequentially producing high tension pulses across spark gap means of said engine comprising a high tension ignition coil including a primary winding and a secondary winding, an electrical energy source connected with said primary winding, means for alternately producing in said primary winding current flow in a first and in a second direction, and for interrupting said current flow between each change of direction of said flow from either one of said directions to the other, at least one pair of spark gap means for said engine connected in circuit with said secondary winding of said high tension ignition coil, first unidirectional current means connected between one of said spark gap means and said secondary winding for enabling current flow to said one spark gap means when current in one direction is induced in said secondary winding and for blocking current flow to said one spark gap means when current flow in an opposite direction is induced in said secondary winding, and second unidirectional current means connected between the other of said spark gap means and said secondary winding for enabling current flow to said other spark gap means when current in said opposite direction is induced in said secondary winding and for blocking current flow to said other spark gap means when current flow in said one direction is induced in said secondary winding.

7. Apparatus according to claim 6 wherein each of said pair of spark gap means includes two spark gap members, with the spark gap members of each pair of spark gap means being connected on opposite sides of said secondary winding and with each spark gap member of one pair being connected in series with one spark gap member of the other pair.

8. Apparatus according to claim 7 wherein: said first unidirectional current means include a pair of first unidirectional current devices connected to enable current flow therethrough when current is induced in said secondary winding in said one direction and to block current flow therethrough when current is induced in said secondary winding in said opposite direction; said second unidirectional current means include a pair of second unidirectional current devices connected to enable current flow therethrough when current is induced in said secondary winding in said opposite direction and to block current flow therethrough when current is induced in said secondary winding in said one direction; and

each of said pair of spark gap means has one of its spark gap members connected to one side of said secondary winding through one of said first or second unidirectional current devices with the other spark gap member of said pair being connected to the other side of said secondary winding through the other of said first or said second unidirectional current devices.

9. Apparatus according to claim 6 wherein said first and said second unidirectional current means comprise diodes.

10. Apparatus according to claim 6 including damping means connected to said high tension ignition coil.

11. Apparatus according to claim 10 wherein said high tension ignition coil includes a core member of high loss core material operating as damping means,

12. Apparatus according to claim 10 wherein said damping means is connected in parallel with said primary winding of said ignition coil.

13. Apparatus as recited in claim 12, including an ohmic resistor as damping means.

14. Apparatus as recited in claim 12, including a voltage-dependent resistor as damping means.

15. Apparatus as recited in claim 12, including a capacitor as damping means.

16. Apparatus as recited in claim 12, including a triac as damping means, the firing electrode of said triac connected to a pulse transmitter such that said triac is fixed at the beginning of a second half-wave produced during the discharge of said high tension coil, to shortcircuit all following resonance oscillations which could lead to undesireable ignition of a spark gap.

17. Apparatus as recited in claim 12, using a triac in a dimmer circuit as clamping means.

18. Apparatus as recited in claim 12, wherein said damping means includes a bridge rectifier in conjunction with a circuit arrangement connected to said bridge output, which circuit comprises a first resistor and a capacitor in series connected to the said output,

and a series circuit connected in parallel therewith consisting of a second resistor, a junction transistor, and a third resistor, and finally, a thyristor connected in parallel with both series circuits, the firing electrode of said transistor being connected to the connecting point between said first resistor and said capacitor such that the drop in voltage appearing across said third resistor acts as a firing voltage for said thyristor.

19. Apparatus as recited in claim 6, wherein said circuit arrangement in said primary circuit of said high tension coil comprises electronic switches.

20. Apparatus as recited in claim 19, wherein said electronic switches are two transistors.

21. Apparatus as recited in claim 20, wherein the collector of one transistor is connected to one end of said primary winding of said high tension coil and the collector of the other transistor to the other end of said primary winding, whilst the emitters of both transistors are connected to earth, and said primary winding has a centre tap which is connected to the unearthed pole of a voltage source.

22. Apparatus as recited in claim 21, wherein the base of each said transistor is connected through a resistor to a voltage normally blocking said transistor, and through a respective switch to a potential capable of switching said transistor on.

23. Apparatus as recited in claim 21, wherein each of the inputs switching said transistors is connected through a series resistor to the base of each of said transistors and to respective zener diodes limiting the control voltage applied to said transistors, whilst a bias resistor is provided between the emitter of each transistor and earth, so that the current in the primary winding of said high tension coil reaches a maximum value which is independent of an operating voltage.

24. Apparatus as recited in claim 21, wherein the collector of each transistor is connected through a blocking diode to a respective end of the primary winding of said high tension coil such that said blocking diodes prevent conduction of said transistors in the current flow direction opposite to the normal conducting direc- 

1. A method for distributorless cyclic ignition of an internal combustion engine by sequentially producing from an energy source high tension pulses across a plurality of spark gap means comprising the steps of alternately inducing current to flow in a first and in a second direction in the primary winding of a high tension ignition coil, interrupting said current flow between each change of direction of said flow from either one of said directions to the other, providing at least one pair of spark gap means connected in circuit with a secondary winding of said high tension ignition coil, blocking current flow to one of said spark gap means while enabling current flow to the other of said spark gap means when said secondary winding has induced therein current flow in a given direction, and blocking current flow to said other spark gap means while enabling current flow to said one spark gap means when the direction of current flow through said secondary winding is reversed.
 2. A method according to claim 1 wherein a plurality of pairs of spark gap means are provided and wherein current flow is blocked to one of the spark gap means of each of said pair while enabling current flow to the other spark gap means of each of said pair when said secondary winding has induced therein current flow in a given direction, and wherein current flow is blocked to the other spark gap means of each of said pairs while enabling current flow to said one spark gap means of each of said pairs when the direction of current flow through said secondary winding is reversed.
 3. A method according to claim 1 including the step of damping resonant oscillations in said high tension coil.
 4. A method according to claim 3 wherein said damping of said resonant oscillations is performed in a primary circuit including the primary winding of said high tension coil.
 5. A method according to claim 4 including the step of short-circuiting the primary circuit including said primary winding of said high tension coil during the appearannce of undesirable resonant oscillations therein.
 6. Apparatus for effecting distributorless cyclic ignition of an internal combustion engine by sequentially producing high tension pulses across spark gap means of said engine comprising a high tension ignition coil including a primary winding and a secondary winding, an electrical energy source connected with said primary winding, means for alternately producing in said primary winding current flow in a first and in a second direction, and for interrupting said current flow between each change of direction of said flow from either one of said directions to the other, at least one pair of spark gap means for said engine connected in circuit with said secondary winding of said high tension ignition coil, first unidirectional current means connected between one of said spark gap means and said secondary winding for enabling current flow to said one spark gap means when current in one direction is induced in said secondary winding and for blocking current flow to said one spark gap means when current flow in an opposite direction is induced in said secondary winding, and second unidirectional current means connected between the other of said spark gap means and said secondary winding for enabling current flow to said other spark gap means when current in said opposite direction is induced in said secondary winding and for blocking current flow to said other spark gap means when current flow in said one direction is induced in said secondary winding.
 7. Apparatus according to claim 6 wherein each of said pair of spark gap means includes two spark gap members, with the spark gap members of each pair of spark gap means being connected on opposite sides of said secondary winding and with each spark gap member of one pair being connected in series with one spark gap member of the other pair.
 8. Apparatus according to claim 7 wherein: said first unidirectional current means include a pair of first unidirectional current devices connected to enable current flow therethrough when current is induced in said secondary winding in said one direction and to block current flow therethrough when current is induced in said secondary winding in said opposite direction; said second unidirectional current means include a pair of second unidirectional current devices connected to enable current flow therethrough when current is induced in said secondary winding in said opposite direction and to block current flow therethrough when current is induced in said secondary winding in said one direction; and each of said pair of spark gap means has one of its spark gap members connected to one side of said secondary winding through one of said first or second unidirectional current devices with the other spark gap member of said pair being connected to the other side of said secondary winding through the other of said first or said second unidirectional current devices.
 9. Apparatus according to claim 6 wherein said first and said second unidirectional current means comprise diodes.
 10. Apparatus according to claim 6 including damping means connected to said high tension ignition coil.
 11. Apparatus according to claim 10 wherein said high tension ignition coil includes a core member of high loss core material operating as damping means,
 12. Apparatus according to claim 10 wherein said damping means is connected in parallel with said primary winding of said ignition coil.
 13. Apparatus as recited in claim 12, including an ohmic resistor as damping means.
 14. Apparatus as recited in claim 12, including a voltage-dependent resistor as damping means.
 15. Apparatus as recited in claim 12, including a capacitor as damping means.
 16. Apparatus as recited in claim 12, including a triac as damping means, the firing electrode of said triac connected to a pulse transmitter such that said triac is fixed at the beginning of a second half-wave produced during the discharge of said high tension coil, to short-circuit all following resonance oscillations which could lead to undesireable ignition of a spark gap.
 17. Apparatus as recited in claim 12, using a triac in a dimmer circuit as damping meAns.
 18. Apparatus as recited in claim 12, wherein said damping means includes a bridge rectifier in conjunction with a circuit arrangement connected to said bridge output, which circuit comprises a first resistor and a capacitor in series connected to the said output, and a series circuit connected in parallel therewith consisting of a second resistor, a junction transistor, and a third resistor, and finally, a thyristor connected in parallel with both series circuits, the firing electrode of said transistor being connected to the connecting point between said first resistor and said capacitor such that the drop in voltage appearing across said third resistor acts as a firing voltage for said thyristor.
 19. Apparatus as recited in claim 6, wherein said circuit arrangement in said primary circuit of said high tension coil comprises electronic switches.
 20. Apparatus as recited in claim 19, wherein said electronic switches are two transistors.
 21. Apparatus as recited in claim 20, wherein the collector of one transistor is connected to one end of said primary winding of said high tension coil and the collector of the other transistor to the other end of said primary winding, whilst the emitters of both transistors are connected to earth, and said primary winding has a centre tap which is connected to the unearthed pole of a voltage source.
 22. Apparatus as recited in claim 21, wherein the base of each said transistor is connected through a resistor to a voltage normally blocking said transistor, and through a respective switch to a potential capable of switching said transistor on.
 23. Apparatus as recited in claim 21, wherein each of the inputs switching said transistors is connected through a series resistor to the base of each of said transistors and to respective zener diodes limiting the control voltage applied to said transistors, whilst a bias resistor is provided between the emitter of each transistor and earth, so that the current in the primary winding of said high tension coil reaches a maximum value which is independent of an operating voltage.
 24. Apparatus as recited in claim 21, wherein the collector of each transistor is connected through a blocking diode to a respective end of the primary winding of said high tension coil such that said blocking diodes prevent conduction of said transistors in the current flow direction opposite to the normal conducting direction thereof. 